Nonmagnetic ring composition



, Patented n... i943 UNIT-en STATE PATENT oi-frice- IiI'ONMAGNETIC RING COMPOSITION Barry L. Frevert and when n. Foley, nundelphia, 2a., assignora to The Mldvale Company, Philadelphia, Pa., a corpo ation of Dela- No Drawing. Application August 21. 1943, Serial No. 49am 6 Claims. (01. vszs) In the manufacture of-non-magnetic retaining rings it has always been necessary to usea composition of steel containing an amount of alloy, usually nickel, chromium and manganese, such that the iron takes on the gamma, or facecentered cubic type of crystalline form which is non-magnetic and little subject to modification by heat treatment. The strength of such an alloy steel is not materially aflected by the process of quenching and tempering in the manner com,

monly used in the hardening of ordinary steels. Strength, however, is an important attribute vof non-magnetic steels and it has been necessary to increase the inherent strength of non-magnetic steels used as retaining rings by deformation at slightly elevated temperatures, a process not so easily carried out with the masses involved as it is inl the production of wireand sheet ofaustenitic stee The extent to-which the strength and hardness of a metal may be increased by the process of deforming at low tem'peraturesis dependent not only on the degree of. deformation and the temperature at which deformationtakes place, but also on the thickness of the metal. In'heavy masses the cheats of deformation tend ordinarily to be confined to the surface layers, whereas in thin material the effects readily penetrate throughout the section. In thick sections itis not unusual to find high tensile strength in the -sur-' face metal and very much lower strength in the deep-seated layers of aforging.

Compositions of steel known to respond in a manner to the strengthening effect of deformation at low temperature and to be practically nonmagnetic have' the following composition range:

The following are specific examples of compo? sitions. within the above ranges:

0 Mn 8i .Ni- Or w Mo A .58 5.33 9.03 5.32 .15 .52 .70 6.60 am 4.80 .10 .as

The silicon content is immaterial and may be that common in carbon steel, say not less than about .15% and not over about 1%. 1

By finishing forging such a composition of austenitic steel at temperatures in the neighborhood of 1200" F. a high tensile strength may be produced together with an adequate degree of V ductility'asmeasured by the percentage of elongation and of reduction of area of the metal when ruptured undertension stresses. The results produced, however, are frequently of such a nature as to be quite misleading in at least two respects: First, the effects of the deformation .at low forging temperature are frequently found to have been confined to the surface metal:

and, secondly, the yield strength of the metal is not increased at the same rate as is the tensile strength and does not therefore attain values frequently demanded by the stresses imposed by service conditions. The yield point of the metal is of great importance. since the rings under disi lustrates the tensile bars.

cussion are usually subject to high speed revolution, in service and failure is likely to be disastrous. Not only is it of the utmost importance that the Y. P. should be as high as possible, but it is also of importance that the Y. P. should have a high'percentage rate relative to the T. S.

A widespread between '1. 8. and Y. P. isa-defect V Y frequently found in the inner properties of rings deformed at low forging temperature. I

The undesirable quality above described may be illustrated by actual cases of rings from the heats A, B and C above listed. The properties, abso-- lute and relative, of I25. and Y. P. exhibited in a surface metal test when finished forged were satisfactory. For example. such a test from heat A showed T. S. 144,000 p. 8-. i. and Y. 1?. 114,000

p. s. i. However, test bars taken-deeply within A the ring showed '1'. s. 114.000 p. s. i. This test ilgreat loss of T. 8. in deeply seated As illustrative of the wide spreads that frequently occur between I. S. a'ndY. P. may be cited tests made of material deeply within retainin rings from heats B and C.

T. B. Y. P. Elong. Bed. of area I P. a. i. P. s. 1. Percent Percent B 150, 000/1Ei, 750 112,000 26. /34. 0 28. 2/34. 7 C- 130, (DO/134, W 76, 000/81, 000 26/33 33. 0/39. 0-

These tests illustrate the wide spread between former varying from 60 to '74 We have found that the addition of .05 to .3% nitrogen to alloys of the above type has profoundly beneficial efl'ects. Not only does it increase the Y. P but it enables the high T. S. and Y. P. combination to be attained without having to carry deformation at temperatures as low as have been required heretofore and produces properties that are high throughout the section with little danger of being misled by the appearance of high strength in the exterior of a forging.

As'typi'cal examples of improvements effected by addition of nitrogen to the material may be cited tests made with rings of the following compositions: 7

0 Mn 81 'Ni Cr Mo w Nadded Two rings were made from heat D and two from heat E, the tests being made of material deeply within the ring, with the following results:

Bed. of '1. S. Y. P. Elong. area P. a. i. P. s. I. Percent Percent D 142 bill/152, 000 114, 000/124, 000 18. 7/26. 22. 4/29. 1 Average- 146, 700 121, 600 19. 5 25. l D 146, 000/155, 000 116, 500/130, 000 25. 6/38. 0 26. 8/41. 3 Avorage 149, 700 124, 200 29. 5 .4 E 121, 500 97, 43. 2 52. 5 E 121, 500 96. 500 43. 2 54. 0

Comparing the tests on B and D, it will be noted that even though B showed a T. S. comparable with (somewhat higher than) D, it showed a much lower Y. P.; the percentage rates of Y. P. to '1'. B. being less than 74% for B as contrasted I with over 83% for D.

less than 75% of'the T. 3., while with N: added the Y. B. will in most compositions run substantially over 75% and usually between 78% and 85% of the T. S.

- although the method'of adding the nitrogen is a T. S. and Y. P., the percentage of the latter to the A convenient method of adding the nitrogen is by means of nitrogen-bearing farm-chromium,

not a determining factor in the result obtained. It should be understood, however, that the per- .centage of nitrogen shown by analysis of the rings may be considerably less than the'amount of nitrogen added. With nitrogen added in percentages from .05 to .3%, the percentage of nitrogen in the final composition will vary from about .03 to the amounts of the loss varying, roughly,- but by no means exactly, in proportion to the amounts of the additions.

-What we claim and desire to protect by Letter's Patent is:

1. A ferrous alloy of low magnetic permeability capable in thick sections of developing, by

working at moderately low temperatures, a high tensile strength, a high yield point and a yield point which is high relative to the tensile strength, 'deeply within, as well as near the surface, said alloy having a composition comprising carbon .05 to 1%, manganese 5 to 10%, silicon .15 to 1%. nickel 8 to 11%, chromium 4 to 8%, metals of the group comprising molybdenum and tungsten 25 to 3%, nitrogen .03% to .25%, and substantially all the remainder iron with its normal impurities,

and characterized by having a yield point substantially exceeding 75% of its tensile strength.

2. A ferrous alloy of low magnetic permeability capable in thick sections of developing, by working at moderately low temperatures, a high tensile strength, a high yield point and a yield point which is high relative to the tensile strength, deeply within, as well as near the surface, said alloy having a composition comprising carbon .05 to 1%, manganese'5 to 10%, silicon .15'to 1%. nickel 8 to 11%, chromium 4 to 8%, metals of the group comprising molybdenum and tungsten .25 to 3%, nitrogen .03 to 25%, and substantially all the remainder iron with its normal impurities, and characterized by having a yield point between about '78 and 85% of the tensile strength.

3. As a new article of manufacture, a non-magnetic ring composed of the ferrous alloy specified in claim 1 and having throughout its entire mass the yeld point-tensile strength ratio specified in claim 1.

4. As a new article of manufacture, a non-magnetic ring composed of the ferrous alloy specified in claim 2 and having in regions thereof most distant from the surface a yield point substantially exceeding of its tensile strength.

5. As a new article of manufacture, a non-magnetic ring composed of the ferrous alloy specified in claim 2 and having throughout its entire mass the yield point-tensile strength ratio specified in claim 2; I

6. As a new article of manufacture, a non-magnetic ring composed of the ferrous alloy specified in claim 2 and having in regions thereof most distant from the surface a yield point between about 18 and of the tensile strength.

HARRY L. FREVERT. FRANCIS B. 

